Doppler ultrasonic measurement of cardiac output: reproducibility and validation.

The Doppler ultrasonic estimation of cardiac output in man is reviewed. Minimal requirements for accurate measurements are discussed, and the published results of reproducibility studies and validation studies are summarized and analysed. Analysis of Doppler records has a coefficient of repeat determination of 5-8% for aortic or LV outflow tract measurements and this is higher for other sites. Short-term variability varies from 4 to 10%, and that over days to weeks from 9 to 14%. Thus a single measurement may vary up to +/- 28% over time with no true change in cardiac output. For cardiac output determination, the Doppler methods show accuracies varying from 10 to 22% (coefficient of variation of the differences between methods) indicating that a single aortic based measurement only reliably lies within +/- 28% compared with other 'standard' methods, and during exercise the accuracy is less (+/- 44%). Doppler methods are safe, fairly reproducible and reasonably accurate methods for measuring cardiac output in selected patients provided signal quality is adequate during recording.